Process for the preparation of benzotrifluorides which are substituted by fluorine and optionally in addition by chlorine, and new benzotrifluorides

ABSTRACT

Benzotrifluorides substituted by fluorine and optionally in addition by chlorine, some of which are new, are prepared by hydrogenating benzotrifluorides which are substituted by fluorine and chlorine, in the presence of a catalyst and a hydrogen chloride acceptor.

This is a division of application Ser. No. 220,038, filed July 15, 1988,now U.S. Pat. Ser. No. 4,885,415.

The present invention relates to a process for the preparation ofbenzotrifluorides which are substituted by fluorine and optionally inaddition by chlorine by selectively hydrogenating benzotrifluorideswhich contain fluorine and chlorine, and to new benzotrifluoridesaccessible in this way.

To date, fluorinated benzotrifluorides have generally been prepared fromchlorobenzotrifluorides by replacing the chlorine of the latter byfluorine for example, using potassium fluoride, (see G. Fuller, J. Chem.Soc. 1965. 6264; J. P. Kolenko et al., Zh. Obsch Khim. 37. 1686 (1967)and EP-A No. 34,402). In a chlorine/fluorine exchange of this type, theactivated chlorine atoms in the o- and p-position relative to the CF₃group can be replaced relatively easily, while the Cl atoms inm-position can be replaced by fluorine only with great difficulty. Acertain pattern of the fluorine substituents in the desired product thusrequires that corresponding chlorine compounds are available. However,the chlorination of benzotrifluoride proceeds by an equation which isdetermined by the influencing action of the CF₃ group and which, in somecases, renders it impossible to obtain certain substitution patterns(see A. H. Usahakov et al., Zh, Organ Khim. 12, 2204 (1976) and 20, 2187(1984)). These include, for example, 2,4,6-trichlorobenzotrifluoride and2,3,4,6-tetrachlorobenzotrifluoride. There is therefore still a demandfor a simple process for the preparation of fluorinatedbenzotrifluorides which avoids these difficulties.

A process has now been found for the preparation of benzotrifluorideswhich are substituted by fluorine and optionally in addition by chlorinewhich is characterized in that benzotrifluorides containing fluorine andchlorine are hydrogenated in the presence of a catalyst and in thepresence of a hydrogen chloride acceptor.

In the process according to the invention, benzotrifluorides whichcontain fluorine and chlorine and which correspond to the formula (I)##STR1## in which m stands for an integer from 1 to 4 and

n stands for an integer from 1 to 5-m

can, for example, be employed.

The starting benzotrifluorides preferably contain 2 to 4 fluorine atomsand 1 to 2 chlorine atoms. The chlorine atoms in these compounds arepreferably in the ortho or meta position relative to the CF₃ group,particularly preferably in the meta position. Particularly preferredstarting benzotrifluorides are2,3,4,6-tetrafluoro-5-chlorobenzotrifluoride,2,4,6-trifluoro-3,5-dichlorobenzotrifluoride,2,4-difluoro-3,5-dichlorobenzotrifluoride,3,4-difluoro-5-chlorobenzotrifluoride,2,3,4-trifluoro-5chlorobenzotrifluoride,4,5-difluoro-2-chlorobenzotrifluoride,2,4-difluoro-5-chlorobenzotrifluoride and2,4-difluoro-3-chlorobenzotrifluoride.

Suitable initial benzotrifluorides for the process according to theinvention can be prepared, for example, by firstly chlorinatingbenzotrifluoride and then replacing some of the chlorine atomsintroduced by fluorine atoms by reaction with potassium fluoride (see,for example, G. Fuller, J. Chem. Soc. 1965, 6264, J. P. Kolenko et al.,Zh. Obsch. Khim. 37, 1686 (1967) and EP-A No. 34,402).

Suitable catalysts are hydrogenation catalysts known in principle, forexample those which contain elements of the subgroup VIII of theperiodic table in the form of metals or in the form of compounds.Particularly suitable are nickel, platinum, palladium and theircompounds, for example in the form of Raney nickel, metallic platinum,metallic palladium and palladium tetra- triphenylphosphine). It is alsopossible for the catalytically-active substance to be applied to supportmaterials, for example to activated charcoal, silica, alumina, silicatesor alkaline earth metal sulphates.

Preferred catalysts are Raney nickel and metallic palladium on activatedcharcoal.

Alternatively, the catalysts can consist of several components and can,for example, also contain promoters, which may also be elements andcompounds other than those of the metals of the subgroup VIII of theperiodic table

The amount of catalyst is generally not crucial. For example, it can be0.01 to 15% by weight relative to the employed benzotrifluoride.Preferably, this amount is 0.1 to 10% by weight. "Catalyst" is taken tomean the active catalyst, hence in the case of support catalysts onlythe active metal.

The hydrogenation is generally carried out in the presence of solventsor diluents. It is not absolutely necessary for these to be capable ofcompletely dissolving the materials employed, since it is also possiblefor a two-phase substrate to be hydrogenated. For example, the startingbenzotrifluoride and/or the hydrogen chloride acceptor can be presentpartly or completely in suspended form during hydrogenation. Suitablesolvents and diluents are, for example, organic acids, such as aceticacid; alcohols, such as methanol, ethanol, propanol and isopropanol;ethers, such as tetrahydrofuran; nitriles, such as acetonitrile, andwater.

Suitable hydrogen chloride acceptors are a wide variety of inorganic andorganic bases, for example, the hydroxides, carbonates, acetates andammonium salts of the alkali metals and alkaline earth metals, andamines, in particular tertiary amines. Sodium acetate, triethylamine,N,N-dimethylaniline, pyrimidine and picoline are preferred.

The hydrogen chloride acceptor can be employed in various amounts.Preferably, at least 0.8 equivalent of hydrogen chloride acceptor isemployed per equivalent of chlorine atoms to be eliminated from thebenzotrifluoride employed.

If it is intended that all the chlorine atoms present be eliminated fromthe benzotrifluoride employed, the upper limit for the amount of thehydrogen chloride acceptor to be employed is not crucial. In this caseit is for practical reasons generally advantageous to employ not morethan 2 equivalents of hydrogen chloride acceptor per equivalent ofchlorine atoms to be eliminated.

If it is not intended that all the chlorine atoms present in thebenzotrifluoride employed be eliminated, i.e., if it is intended toprepare benzotrifluorides which still contain chlorine atoms, then oneshould not employ considerably more hydrogen chloride acceptor than isstoichiometrically required. In this case, preferably up to 1.2,particularly preferably up to 1.05 and very particularly preferably 1equivalent of hydrogen chloride acceptor are, or is, employed perequivalent of chlorine atoms to be eliminated.

The hydrogenation according to the invention can, for example, becarried out at pressures in the range from atmospheric pressure to 200bar and temperatures in the range from 20° to 200° C. Pressures in therange from atmospheric pressure to 120 bar and temperatures in the rangefrom 50° to 140° C. are preferred.

In the case of complete dechlorination of the starting material, thereaction according to the invention is complete when hydrogen is nolonger taken up, and, in the case of selective dechlorination, when theamount of hydrogen required stoichiometrically has been taken up.

Working up of the reaction mixture can be carried out in a simple mannerFor example, the procedure can be such that, firstly, the solidconstituents of the reaction mixture (in general, this is the catalyst,where appropriate, also, for example, the loaded hydrogen chlorideacceptor) are removed by filtration and the prepared benzotrifluoride,which is substituted by fluorine and optionally in addition by chlorine,is obtained from the filtrate by distillation.

The benzotrifluoride obtained contains at least 1 chlorine atom lessthan the starting benzotrifluoride. For example, the benzotrifluorideprepared can be a product of the formula (II) ##STR2## in which m'stands for an integer from 1 to 4 and

n' stands for zero or an integer up to 4-m'.

The process according to the invention has the advantage that very pureproducts are obtained in good yields. The starting compounds are easilyaccessible because the replacement of chlorine by fluorine proceeds morereadily in higher-chlorinated benzotrifluorides than inlower-chlorinated benzotrifluorides. The route according to theinvention to give benzotrifluorides which are substituted by fluorineand optionally by chlorine is therefore more advantageous than thedirect introduction of fluorine into unsubstituted benzotrifluorides.Moreover, fluorine-substituted and optionally chlorine-substitutedbenzotrifluorides having substitution patterns which hitherto were notaccessible, or only accessible with difficulty, can be obtained.

In the process according to the invention, it is surprising that thefluorine substituents present on the aromatic ring are not eliminatedand also that virtually no hydrogenation of the aromatic ring takesplace. Moreover, it is surprising that if several chlorine substituentsare present in the starting material, these can be eliminatedindividually with good selectivities.

The present invention furthermore relates to fluorine-substitutedbenzotrifluorides of the formula (III) ##STR3## in which X₁ stands forfluorine or chlorine and

X₂, in the case of X₁ =fluorine, stands for hydrogen or fluorine, and,in the case of X₁ =chlorine, for fluorine.

The benzotrifluorides of the formula (III) are, in particular,2,3,4,6-tetrafluorobenzotrifluoride,2,4,6-trifluoro-3-chlorobenzotrifluoride and2,3,6-trifluorobenzotrifluoride.

The benzotrifluorides of the formula (III) can be prepared as describedabove.

Benzotrifluorides which are substituted by fluorine and optionally bychlorine are important intermediates in the preparation of activecompounds. For example, benzotrifluorides which are substituted byfluorine and optionally by chlorine and which can be obtained accordingto the present invention can be reacted with hydrazine hydrate, and thearyl hydrazines obtainable in this reaction can be reacted with1,3-diketones of the formula (IV) ##STR4## in which R₁ and R₃ stand foralkyl and

R₂ stands for alkyl or halogenoalkyl

and 3,5-dialkyl-1-aryl-pyrazoles of the formula (V) ##STR5## in which R₁to R₃ have the meaning given in formula (IV) and

Ar stands for a fluorinated and optionally chlorinated benzotrifluorideradical

can thus be obtained.

From compounds of the formula (V), compounds of the formula (VI)##STR6## in which R₁ to R₃ and Ar have the meaning given in formula (V)and

m stands for 1 or 2 can be prepared by oxidation in a customary manner.

The compounds of the formulae (V) and (VI) are distinguished by a stronginsecticidal action, for example against insects which are harmful toplants, such as the larvae of the mustard beetle. They also have astrong action against hygiene and stored-product pests, such as thecommon house fly (Musca domestica) and against parasites of warm-bloodedanimals, such as the autumn fly (Musca autumnalis)

Examples EXAMPLE 1

1 mol of starting material in 1 l of acetic acid together with 1.05 molof sodium acetate per mol of chlorine to be eliminated were initiallyintroduced into a hydrogenation apparatus 10 g of catalyst (5% by weightof metallic palladium on activated charcoal) were then added, and themixture was subsequently hydrogenated at a hydrogen pressure of 30 to 50bar at 12° C. until the pressure remained constant. The catalyst wasthen separated from the reaction mixture by filtration, and the filtratewas distilled via a column. The distillate was washed with water inorder to remove small amounts of acetic acid. The reaction product had apurity of more than 98% in each case. Further details can be seen fromTable 1.

                                      TABLE 1                                     __________________________________________________________________________    Ex-                                Refractive                                                                          Yield                                ample                                                                             Starting material                                                                          Product    Boiling point                                                                        index % of                                 No. (. . . -benzotrifluoride)                                                                  (. . . benzotrifluoride)                                                                 at 1013 mbar                                                                         n.sub.D.sup.20                                                                      theory                               __________________________________________________________________________    1a  5-Chlorotetrafluoro-                                                                       2,3,4,6-Tetrafluoro-                                                                     105-106° C.                                                                   1.3770                                                                              92                                   1b  3,5-Dichlorotrifluoro-                                                                     2,4,6-Trifluoro-                                                                         104° C.                                                                       1.3840                                                                              83                                   1c  3,5-Dichlorotrifluoro-                                                                     3-Chloro-2,4,6-trifluoro-                                                                145° C.                                                                       1.4170                                                                              76                                   1d  3,5-Dichloro-2,4-difluoro-                                                                 2,4-Difluoro-                                                                            105-106° C.                                                                   1.3968                                                                              84                                   1e  5-Chloro-3,4-difluoro-                                                                     3,4-Difluoro-                                                                            103-104° C.                                                                   1.3958                                                                              85                                   1f  5-Chloro-2,3,4-trifluoro-                                                                  2,3,4-Trifluoro-                                                                         105-106° C.                                                                   1.3842                                                                              89                                   1g  3-Chloro-2,5,6-trifluoro-                                                                  2,3,6-Trifluoro-                                                                         105-107° C.                                                                   1.3850                                                                              82                                   __________________________________________________________________________

EXAMPLE 2

216 g (1 mol) of 2-chloro-4,5-difluorobenzotrifluoride in 1 1 ofmethanol were initially introduced into a hydrogenation apparatus, and110 g of triethylamine and 15 g of Raney nickel were added. Thehydrogenation apparatus was then flushed using hydrogen and then warmedto 80° C., and a pressure of 100 bar of hydrogen was applied. After thehydrogen pressure had dropped, it was restored again to 100 bar, and themixture was allowed to react until the pressure remained constant. Aftercooling, the pressure was released, and the reaction mixture wasfiltered. The filtrate was diluted using 3 1 of water, and the organicphase was separated off. The latter was dried and distilled via acolumn. 147 g of 3,4-difluorobenzotrifluoride having a boiling point of108° to 109° C. at 1013 mbar and a refractive index n_(D) ²⁰ of 1.3973were obtained.

EXAMPLE 3

The procedure as in Example 2 was followed, but 1 mol of5-chloro-2,4-difluorobenzotrifluoride was employed, and 151 g of2,4-difluorobenzotrifluoride having a boiling point of 105° to 106° C.at 1013 mbar and a refractive index n_(D) ²⁰ of 1.3970 were obtained

EXAMPLE 4

100 g of 3-chloro-2,4-difluorobenzotrifluoride in 500 ml of acetonitrileand 60 g of pulverulent sodium carbonate were initially introduced intoa hydrogenation apparatus equipped with a diffuser stone and a stirrer.10 g of catalyst (5% by weight of metallic palladium on activatedcharcoal) were then added, and hydrogen was passed in at 80° C. for 10hours Subsequently, the batch was cooled and filtered, and the filtratewas distilled via a column packed with perforated rins made of stainlesssteel. 56 g of 2,4-difluorobenzotrifluoride having a boiling point of105° to 106° C. at 1,030 mbar were obtained. The refractive index n_(D)²⁰ was 1.3968.

EXAMPLE 5

300 g of 3,5-dichloro-2,6-difluorobenzotrifluoride in 1,200 ml of aceticacid and 210 g of sodium acetate were initially introduced into ahydrogenation apparatus, 10 g of 5% palladium on A-charcoal were added,and the batch was hydrogenated at a hydrogen pressure of 30 to 50 bar at80°-120° C., after the apparatus has been flushed with hydrogen. Afterthe hydrogen uptake had ended (constant pressure), the batch was cooled,the catalyst was filtered off by suction, and the solution was stirredwith 2 1 of water. The organic phase which separated was removed anddistilled. Boiling point: 106°-107° C.; n_(D) ²⁰ : 1.3972; yield 193 gof 2,6-difluorobenzotrifluoride.

What is claimed is:
 1. 2,4,6-Trifluoro-3-chlorobenzotrifluoride. 2.2,3,6-Trifluorobenzotrifluoride.